A study of fathers in the Philippines so hot and fresh that if it were a waffle it would burn a hole into the roof of your mouth and melt all your fillings (you really should have flossed) suggests that new dads who sleep in close proximity to their kids experience temporary decreases in testosterone. Though the study is by no means conclusive (nor are researchers entirely sure their work applies to dads outside of the Philippines), it does suggest, according to LiveScience, that our traditional concept of arm-wrestling, water-buffalo-tackling masculinity is in for a thorough evolutionary biology revision.

Researchers found that fathers who slept next to or in the same room as their kids temporarily had lower levels of testosterone than fathers who slept in separate rooms. Further, those testosterone levels returned to normal once fathers woke and their infants could no longer exert their incubus-like, man-energy-sapping powers. Though the four-year study comes with many caveats (including cultural differences between the Philippines, where fathers more commonly sleep with their kids, and the United States), it also suggests that men's bodies make adjustments just the same as women's bodies in order to better adapt to child rearing.

Study researcher Lee Gettler from the University of Notre Dame notes that the study "suggests to us that active fatherhood has a deep history in the human species and our ancestors." The drop in testosterone, for example, might have helped (and still helps) many new fathers transition from roles like supreme bloodsport champion and mastodon hunter to the calmer, gentler role of nurturer.

The study has quite a few limitations, most notably the fact that co-sleeping has been pretty widely stigmatized in the U.S. as a dangerous practice, with critics warning that bed-sharing with an infant increases the risk of accidental suffocation. Sleeping arrangements for many of the 362 new fathers participating in the study were also starkly different from sleeping arrangements in the U.S., with many men sleeping on mats, blankets or mattresses placed directly on the floor. Sleeping next to a newborn also makes for a more restive night, and such tossing and turning might be responsible for at least some of the variations in testosterone levels (though Gettler also noted that most men in the study reported having good sleeping habits).